In the construction industry trenches, pits and other types of open excavations require the use shoring devices. Various known shoring devices include vertical rail posts, shoring panels and horizontal spreaders pressing the shoring walls against the side wall of the trench. Such shoring devices are called ‘Slide Rail Shoring Systems’.
Previous slide rail shoring systems as disclosed in U.S. Pat. Nos. 3,910,053 and 4,657,442 (Krings) use a rail post having individual formlocking channel connections of ‘C’ type for sliding the panels. The load developed by the active pressure of the excavation walls is spread on very limited areas of contact between the post and panel. The stresses are highly concentrated at these areas becoming sources of high friction and temperature during the installation and removal of the system. Thus, damage is caused to both rail post and the panel, which strongly limits the application of such a system in pipeline productions, where the installation and removal of the system are effectuated continuously.
U.S. Pat. Nos. 5,310,289 and 5,503,504 (Hess et al.), disclose a rail post having a unique channel for a maximum of two shoring walls, created by an outer panel and an inner panel. Only the outer panel slides formlockingly within the post; the inner panel is completely free and slides inside the outer panel and the rail posts. The design of the inner panel presents a risk of kicking in the trench when adjacent rail posts are not plumb. This is an important safety concern for the worker inside the trench. This phenomenon becomes prominent when the depth of excavation is over 20′ deep. On the other hand, shoring of excavations over 16′ deep requires the stacking and connection of two or more panels, which later must be removed at once. Removing two or more panels at once is a very difficult task and sometimes even impossible to accomplish even when heavy duty equipment is used. Yet another concern faced by this design is the difficulty of removing the inner panel when the deflection of the upper panel has begun. Also, it should be noted that a slide rail shoring system using differing types of panels requires a much bigger inventory of panels than a system that uses interchangeable panels.
U.S. Pat. No. 3,950,952 (Krings), U.S. Pat. Nos. 5,310,289 and 5,503,504 (Hess et al) disclose very similar strut frames having a rectangular structure where the vertical members are equipped with rollers. These frames are designed to slide vertically between opposite rail posts in order to support the load coming from either side of the shoring walls. From an engineering standpoint, a frame having a rectangular cell is not a stable structure because it allows deformations without affecting the length of its members. For example, a rectangular cell may twist into a parallelogram. Additionally, the lower horizontal strut of the frame diminishes the pipe culvert thereby requiring special solutions for the installation of pipes having big diameters or of big box culverts.